Machinable glass-ceramics

ABSTRACT

Micaceous glass-ceramics are useful in the fabrication of single and multi-unit dental restorations including but not limited to orthodontic appliances, bridges, space maintainers, tooth replacement appliances, splints, crowns, partial crowns, dentures, posts, teeth, jackets, inlays, onlays, facing, veneers, facets, implants, abutments, cylinders, and connectors by machining the glass-ceramic using CAM/CAM devices. The micaceous glass-ceramics are provided in a plurality of shades and colors to adequately match the colors and shades of teeth found in 95% or more of the human population.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Provisional ApplicationSerial No. 60/125,506 filed on Mar. 19, 1999 which is herebyincorporated by reference.

FIELD OF THE INVENION

[0002] This invention relates generally to a glass powder, which iscrystallizable and forms a sintered micaceous glass-ceramic in aplurality of shades and more specifically to micaceous glass ceramics,which are machinable into various dental articles by conventional tools.This material is especially useful for the fabrication of dentalrestorations using computer assisted design/computer assisted milling(CAD/CAM) devices.

BACKGROUND OF THE INVENTION

[0003] Micaceous glass-ceramic materials (i.e.glass-ceramics comprisinga crystalline phase that belongs to the mica family such as tetrasilicfluormicas or fluorophlogopite micas) are known to exhibit excellentmachinability. However, their use as CAD/CAM materials for dentistry islimited by the inability to produce the required range of shades andtranslucency paramount for esthetically sound restorations. Thisseverely inhibits widespread use of micaceous materials as dentalrestoratives considering that the driving force for all-ceramicrestorations is esthetics superior to that of porcelain fused-to-metal(PFM) restorations. For example, Dicor MGC, available from DentsplyInternational Inc., Caulk Division, (located in Milford, Del.) is acommercially available micaceous dental ceramic for use in CAD/CAMdevices, but it is supplied in only two modifications, Dicor MGC—Lightand Dicor MGC—Dark. Other limitations of micaceous glass-ceramicsinclude high solubility and low strength in comparison to other dentalceramics. One such example is ProGlass™ ceramic available from CAD/CAMVentures LLC, (located in Irving, Tex.), which is a sugary-whitemica-containing material exhibiting a flexure strength of about 100 toabout 150 MPa and a solubility of about 1 mg/cm² (1000 μM/cm²).

[0004] At the same time, micaceous glass-ceramics exhibit far superiormachinability compared to other CAD/CAM ceramics such as sanidine-basedVita Mark II, available from Vita Zahnfabrik (Germany) and leucite-basedPro-Cad from Ivoclar (Lichtenstein), as set forth in “MechanicalProperties of a New Mica-Based Machinable Glass Ceramic For CAD/CAMRestorations” by J. Y. Thompson et al., The Journal of ProstheticDentistry, 1996, Vol. 76, No. 6, 619-623 and “Machinable Glass-CeramicsBased on Tetrasilicic Mica” by D. G. Grossman, Journal of Am.Cer.Soc.,1972, Vol. 55, No. 9. The latter two above-mentioned ceramics can bemachined by diamond tools only and require wet processing in contrast tomicaceous glass-ceramics such as ProGlass™ which can be machined bycarbide tooling using dry processing which is much more cost-effective.In addition, micaceous glass-ceramics can be much more translucent thanvery opaceous sanidine glass-ceramics U.S. Pat. Nos. 4,652,312,4,431,420 and 5,246,889 are each directed to mica-containing ceramicsthat are formed from glass compositions and are shaped as glass andconverted into micaceous glass-ceramics by conventional volumecrystallization techniques. Each process involves melting glass batches,casting the glass melts into molds, and crystallizing the glass intomicaceous glass-ceramics. There is no discussion providing how toachieve adequate colors and shades to accurately match the color of aperson's tooth or how to control the shading of mica containingglass-ceramics. Any mention of colorants appears to be directed toadding the colorants to the glass batch prior to melting. Such processdoes not effectively control the color of the resulting glass-ceramic.Furthermore, each of the processes appears to effect crystallization byperforming bulk or volume crystallization. It is difficult to controlthe color of the micaceous glass-ceramics when utilizing volumecrystallization. None of the prior art is concerned with the need toprovide a variety of colors and shades to adequately match the color andshade of a patient's teeth.

[0005] It is desirable to provide a variety of shades of micaceousglass-ceramics in order to fabricate restorations that closely andaccurately match the teeth in a patient's mouth. It is preferable toprovide an efficient and effective method of producing a variety ofshades of micaceous glass-ceramics. It is beneficial to providemicaceous glass-ceramics that are machinable and that come in a varietyof shades.

SUMMARY OF THE INVENTION

[0006] These and other objects and advantages are accomplished herein bythe micaceous glass-ceramics comprising silica, magnesium oxide andfluorine in addition to other components listed below. Theglass-ceramics are useful in the fabrication of single and multi-unitdental restorations including but not limited to orthodontic appliances,bridges, space maintainers, tooth replacement appliances, splints,crowns, partial crowns, dentures, posts, teeth, jackets, inlays, onlays,facing, veneers, facets, implants, abutments, cylinders, and connectorsby machining the glass-ceramic using CAM/CAM devices. The micaceousglass-ceramics are provided in a plurality of shades and colors toadequately match the colors and shades of teeth found in 95% or more ofthe human population.

[0007] In accordance with one embodiment directed to the process ofmaking the glass-ceramics, the batch ingredients of the compositions aremelted at a temperature in the range of about 1200° to about 1650° C.,for a time in the range of about 0.5 to about 8 hours, thereafter it isquenched, and pulverized into powder. Pigments, opacifiers, fluorescingagents and the like are mixed with the powder. The powder is then usedto form net-shaped or block-shaped pre-forms or blanks to be used inCAD/CAM devices. Blanks are dry-pressed and sintered using a one- ortwo-step heating cycle at a temperature in the range of about 6000 toabout 1200° C. and for a time in the range of about 0.5 to about 4 hoursfor each step in the cycle. The sintering is preferably conducted in avacuum. Occurring simultaneously with sintering, surface crystallizationof the starting glass powder yields the amount of mica phase of at leastthirty volume percent (30 vol. %) required for machinability as well asstrength.

DETAILED DESCRIPTION OF THE INVENTION

[0008] As will be appreciated, the present invention providesglass-ceramic compositions comprising a glassy matrix and one or moremicaceous phases (e.g., tetrasilic flourmica, fluorophlogopite mica andthe like). The glass-ceramics are useful in the fabrication of dentalrestorations. The micaceous glass-ceramic compositions contain interalia, silica, magnesium oxide and fluorine in the ranges given in Table1 below. The glass-ceramic compositions have a combination of propertiesincluding high strength and chemical durability useful for dentalrestorations. The glass-ceramics have good machinability, i.e., theability to be cut or milled by a cutting tool into a dental restorativeshape that accurately depicts the original shape of the tooth to berestored or replaced.

[0009] In an important aspect herein, the micaceous glass-ceramics areprovided in a plurality of shades and colors to adequately match thecolors and shades of teeth found in 95% or more of the human population.The shades and colors of the glass-ceramics provide the dentaltechnician with the ability to closely and effectively match the colorand shade of the patient's tooth or teeth abutting or adjacent to thetooth or teeth that is/are being restored or replaced. TABLE 1Compositions of the starting glass powder Wt % Wt % Oxide Mole % Range 1Range 2 SiO₂ 30-65 43-72 43-72 Al₂O₃ 0-7  3-14 0-3 B₂O₃ 0-3 0-3 0-3 ZnO0-3 0-3 0-3 CaO 0-5 0-7 0-3 MgO 15-33 10-30 10-30 TiO₂ 0-3 0-3 0-3 BaO +SrO 0-3 0-5 0-5 Li₂O 0-3 0-3 0-3 K₂O  0-10 0-7  7-19 Na₂O 0-7 0-3 0-3CeO₂ + La₂O₃ ₊ 0-1 0-2 0-2 Tb₄O₇ ZrO₂ 0-4  0-10  0-10 F 14-25  5-10 5-10

[0010] In accordance with one embodiment of the method of the invention,the shaded micaceous glass-ceramics are manufactured by admixingpigments and other additives to the starting glass powder. The powder isformed into pre-forms or blanks and the blanks are concurrently sinteredand crystallized. The resulting shaded blanks of various shades andtranslucency levels are consistent with current all-ceramic orporcelain-fused-to-metal (PFM) dental porcelain systems. The pre-formsor blanks may be machined into a dental restoration using a CAD/CAMdevice.

[0011] In accordance with the process, the glass compositions within theranges given in 20 Table 1 are melted at a temperature in the range ofabout 1200° to about 1650° C. and for a time in the range of about 0.5to about 8 hours, thereafter quenched, and pulverized into powder. Thispowder is sieved to obtain the required particle size and mixed withconventional additives such as pigments, opacifiers, and fluorescingagents, which will produce various colors, shades and translucencylevels after sintering and concurrent crystallization have beenperformed. The powder that contains the additives is then used to formnet-shaped or block-shaped pre-forms or blanks to be used in CAD/CAMdevices. The blanks are dry-pressed and sintered using a one- ortwo-step heating cycle at a temperature in the range of about 600° toabout 1200° C. and for a time in the range of about 0.5 to about 4 hoursfor each step in the cycle. The sintering is preferably conducted in avacuum atmosphere. Occurring simultaneously with sintering, surfacecrystallization of the starting glass powder yields an amount of micaphase of at least thirty volume percent (30 vol %) required formachinability as well as strength. Copending commonly assigned U.S.application Ser. No. 09/458,919, filed on Dec. 10, 1999, and U.S. Pat.No. 5,968,856 to Schweiger discuss volume crystallization and surfacecrystallization of lithium disilicate glass-ceramics and are herebyincorporated by reference.

[0012] In mass-production of CAD/CAM blanks, uniaxial pressing or otherforming techniques are utilized, e.g. CIP/HIP route whereby green bodiesare formed in a CIP (Cold Isostatic Press) and subsequently sinteredunder pressure in an HIP (Hot Isostatic Press). As an alternative to theCIP method, the powder can be mixed with binder and pelletized orextruded. Useful CAD/CAM devices include the CERECTM machine (availablefrom Siemens AG), the PROCAMTM machine (available from CAD CAM VenturesLLC in Irving, Tex. ) or copy-milling devices such as the Celay™ machine(available from Mikrona Technologie AG).

[0013] Essential for the present invention is an F content in excess ofabout 14 mole percent (about 5 weight percent). Besides being aconstituent of fluormicas, F facilitates surface crystallization. Otheringredients that favor surface crystallization are B₂O₃, P₂O₅, BaO andLi₂O.

[0014] Essential for the present invention is the volume fraction, sizeand aspect ratio of the mica phase in the resultant sinteredglass-ceramic. The larger the mica plates and the higher their aspectratio, the lower the volume fraction of mica that is required to attainmachinability. An aspect ratio, i.e., ratio of thickness to length, ofthe mica plate of ≧2 is preferred. At least thirty volume percent (30vol. %) of mica is required to attain machinability. At least thirtyvolume percent (30 vol. %) of the residual glass phase is required forsinterability. Therefore, the mica content is between about 30 and about70 volume percent, and preferably between about about 40 and about 60volume percent.

[0015] Some of the compositions of the present invention are extremelyreactive and will dissolve additives (e.g., pigments and fluorescingagents) during sintering of the CAD/CAM blocks. In this case, it wasfound that using coarser additives (e.g., pigments or fluorescingagents) substantially alleviated this problem. Normally, these additives(pigments and fluorescing agents) have an average particle size of about4 to about 8 microns. For most reactive compositions, it was found to becritical to use additives of average particles size equal to orexceeding 15 microns. It is believed that, at the same time, particlesexceeding 60 microns will compromise strength. Thus, special care shouldbe taken to remove particles greater than 60 microns. Preferably, theaverage size of the additives is in the range of about 15 to about 35microns, and more preferably in the range of about 20 to about 30microns.

[0016] Application of pressure during sintering of blanks such as in theCIP/HIP route described above is more expensive than vacuum sintering ofuniaxially pressed blanks but may be extremely beneficial in some cases.For example, the CIP/HIP route allows consolidation of powders havinghigh pigment load, or powders yielding high mica content uponcrystallization, or powders having high ZrO₂ content.

[0017] Extremely beneficial, especially for larger high aspect ratiomica, is post-machining heat treatment of dental restorations attemperatures between the glass transition temperature (GTT) and thedilatometric softening point (DSP). This heat-treatment affects surfacecrack healing and increases structural integrity of the restorations.

[0018] In addition to fluormicas, other phases can be present such ascordierite, apatite, spodumene and zirconia. Consequently the expansionof the resulting glass-ceramic can be varied in the range of about 7 toabout 12×10⁻⁶/° C.

[0019] A coating is preferably applied over the core materialmanufactured from the micaceous glass-ceramic to provide anaesthetically pleasing surface. A suitable coating is a ceramic,glass-ceramic, a glass, a glaze and/or a composite material. It isadvantageous that the coating has a coefficient of thermal expansionslightly less than the thermal expansion of the core material. Thecoating is typically applied by sintering the ceramic, glass-ceramic,glass, glaze a composite material onto the micaceous glass-ceramic core.

[0020] The following examples illustrate the invention.

EXAMPLE 1

[0021] A starting glass composition corresponding to the composition setforth in Table 2 below was batched from conventional raw ingredients andmelted at 1400° C. for 4 hours in a coarse-grained alumina crucible. Theglass melt was quenched into water. The quenched glass was dried andmilled into powder. The powder was screened to −200 mesh. Commercialpigments and fluorescing agents (yellow from Cerdec Co. (Washington,Pa.), pink from Engelhard Corp. (Iselin, N.J.) and jet black fromStandard Ceramic Supply Co. (Carnegie, Pa.)) were added to and blendedwith the powder. The powder was dry-pressed into 18×18×25 mm³ blocks.The blocks were fired in a vacuum of 20 torr using a two-step heatingcycle at 10° C./min to 650° C. and held for 2 hours at this temperatureand 10° C./min to 1100° C. and held for 4 hours at this temperature. Theblocks were sectioned into bars for three-point bend strength tests andsmall squares for solubility measurements according to ISO 9693solubility testing standards. The measurements are listed in Table 2below.

EXAMPLE 2

[0022] A starting glass composition corresponding to composition setforth in Table 2 below was batched from conventional raw ingredients andmelted at 1400° C. for 4 hours in a coarse-grained alumina crucible. Theglass melt was quenched into water. The quenched glass was dried andmilled into powder. The powder was screened to −200 mesh. Commercialpigments and fluorescing agents were used in concentrations given inTable 3 below. Since it is known that all dental shades can be producedby varying combinations of three basic pigments. i.e., yellow, red (orpink) and blue (or gray or black), the glass-ceramic of this example wasshaded using both individual yellow, pink and black pigments and theircombinations. Yellow pigments from Cerdec (Washington, Pa.), pinkpigments from Engelhard Corp. (Iselin, N.J.) and jet black pigments fromStandard Ceramic Supply Co. (Carnegie, Pa.) were used. The powderformulations were pressed into 2.5 gram disks and fired in a vacuum of20 torr using a two-step heating cycle at 10° C./min to 650° C. and heldfor 2 hours at this temperature and 10° C./min to 1100° C. and held for4 hours at this temperature. The resulting shades were evaluated usingthe ColorTec-SCM™ color computer from ColorTec Corp. (Clinton, N.J.) andwere found appropriate for simulating the color and shade of a person'steeth.

EXAMPLE 3

[0023] Blocks of lightly shaded glass-ceramics of Example 2 were sent toCAD CAM Ventures LLC (Irving, Tex.) and to DentalMatic Technologies Inc.(Sainte-Laurent, Quebec, Canada) to be evaluated for machinability. Theywere machined into shapes roughly approaching that of a dental coping.The machinability was evaluated as satisfactory. TABLE 2 Compositions ofglass-ceramics in Examples 1 and 2 Wt % Wt % Oxide Example 1 Example 2SiO₂ 40.8 61.0 Al₂O₃ 11.6 0.5 B₂O₃ 0 0 ZnO 0 0 CaO 5.5 0 MgO 27.4 17.2TiO₂ 0 0 BaO 0 0 Li₂O 0 0 K₂O 1.5 13.1 Na₂O 0 0 CeO₂ 0 0 ZrO₂ 8.3 5 F8.6 5.6 3-Pt bend 196 ± 24 >100 strength (MPa) Iso 9693 8 <100Solubility μg/cm² CTE 8° × 10⁻⁶/° C.) Not (25°-500° C.) Measured

[0024] TABLE 3 Example 2 powder with the addition of pigments. Glasspowder of example Yellow Pink Jet Black CIE L*a*b* 2 41720 D320 K-60Light Source: Wt % Wt % Wt % Wt % D65 - 10° 99.2687 0.7313 L* 53.31 a*−2.47 b* 21.33 C* 21.47 h* 96.62 99.6693 0.3307 L* 55.461 a* 2.10 b*0.22 C* 2.11 h* 6.06 99.995 0.005 L* 54.67 a* −0.31 b* 0.08 C* 0.32 h*164.84 98.6 1.4 99.3 0.7 99.99 0.01 98.933 0.7313 0.3307 0.005 98.59 0.70.7 0.01

[0025] The glass-ceramics of the invention have the capability toprovide a wide selection of shades and colors for matching the shadesand colors of a person's teeth. The glass-ceramics are readilymachinable and provide high strength and chemical durability to thedental restorations made therefrom.

[0026] While various descriptions of the present invention are describedabove, it should be understood that the various features can be usedsingly or in any combination thereof. Therefore, this invention is notto be limited to only the specifically preferred embodiments depictedherein.

[0027] Further, it should be understood that variations andmodifications within the spirit and scope of the invention may occur tothose skilled in the art to which the invention pertains. Accordingly,all expedient modifications readily attainable by one versed in the artfrom the disclosure set forth herein that are within the scope andspirit of the present invention are to be included as furtherembodiments of the present invention. The scope of the present inventionis accordingly defined as set forth in the appended claims.

What is claimed is:
 1. A method of making a micaceous dental materialcomprising: melting a starting glass composition at temperatures withinthe range of about 1200 to about 1650° C.; quenching the glass melt;pulverizing the quenched glass into a powder; forming the glass powderinto pre-forms; and sintering the pre-forms to convert the glass into aglass-ceramic dental material.
 2. The method of claim 1 furthercomprising adding one or more additives selected from pigments,fluorescing agents, opacifying agents and mixtures thereof to the glasspowder prior to shaping the powder into pre-forms.
 3. The method ofclaim 1 wherein the sintered pre-forms are milled into a dentalrestoration.
 4. The method of claim 1 wherein the micaceousglass-ceramic comprises: about 43 to about 72 weight % SiO₂; about 3 toabout 14 weight % Al₂O₃; about 10 to about 30 weight % MgO; and about 5to about 10 weight % F.
 5. The method of claim 1 wherein the micaceousglass-ceramic comprises: about 43 to about 72 weight % SiO₂; about 7 toabout 19 weight % K₂O; about 10 to about 30 weight % MgO; and about 5 toabout 10 weight % F.
 6. The micaceous glass-ceramic of claim 4 furthercomprising: up to about 3 weight % B₂O₃; up to about 3 weight % ZnO; upto about 7 weight % CaO; up to about 5 weight % BaO and SrO; up to about3 weight % Li₂O; up to about 7 weight % K₂O; up to about 3 weight %Na₂O; up to about 2 weight % CeO₂, La₂O₃ and Tb₄O₇; up to about 3 weight% TiO₂;and up to about 10 weight % ZrO₂.
 7. The micaceous glass-ceramicof claim 5 further comprising: up to about 3 weight % Al₂O₃; up to about3 weight % B₂O₃; up to about 3 weight % ZnO; up to about 3 weight % CaO;up to about 5 weight % BaO and SrO; up to about 3 weight % Li₂O; up toabout 3 weight % Na₂O; up to about 2 weight % CeO₂, +La₂O₃+Tb₄O₇; up toabout 3 weight % TiO₂;and up to about 10 weight % ZrO₂.
 8. The method ofclaim 4 wherein the glass-ceramic comprises at least about thirty volumepercent of mica.
 9. The method of claim 5 wherein the glass-ceramiccomprises at least about thirty volume percent of mica.
 10. The methodof claim 1 wherein sintering is conducted under a vacuum.
 11. A methodof making a micaceous dental material comprising: melting a startingglass composition at temperatures within the range of about 1200 toabout 1650° C.; quenching the glass melt; pulverizing the quenched glassinto a powder; adding one or more additives selected from pigments,fluorescing agents, opacifying agents and mixtures thereof to the glasspowder; forming the glass powder into pre-forms; and sintering thepre-forms to convert the glass into a glass-ceramic dental material. 12.A micaceous dental material made from the method of claim
 1. 13. Amicaceous dental restoration made from the method of claim
 3. 14. Amicaceous dental restoration made from the method of claim
 4. 15. Themicaceous dental restoration of claim 13 selected from the groupconsisting of an orthodontic appliance, bridge, space maintainer, toothreplacement appliance, splint, crown, partial crown, denture, post,tooth, jacket, inlay, onlay, facing, veneer, facet, implant, abutment,cylinder, and connector.
 16. The micaceous dental restoration of claim14 selected from the group consisting of an orthodontic appliance,bridge, space maintainer, tooth replacement appliance, splint, crown,partial crown, denture, post, tooth, jacket, inlay, onlay, facing,veneer, facet, implant, abutment, cylinder, and connector.
 17. Amicaceous glass-ceramic for use in the fabrication of a dentalrestoration comprising a variety of colors and shades to adequatelymatch the color and shade of a patient's tooth in the mouth.
 18. Amicaceous glass-ceramic for use in the fabrication of a dentalrestoration comprising a variety of colors and shades to adequatelymatch the colors and shades of teeth found in 95% or more of the humanpopulation.
 19. The micaceous glass-ceramic of claim 18 comprising:about 43 to about 72 weight % SiO₂; about 3 to about 14 weight % Al₂O₃;about 10 to about 30 weight % MgO; and about 5 to about 10 weight % F.20. The micaceous glass-ceramic of claim 18 comprising: about 43 toabout 72 weight % SiO₂; about 7 to about 19 weight % K₂O; about 10 toabout 30 weight % MgO; and about 5 to about 10 weight % F.
 21. Themethod of claim 2 wherein the additives have an average particle sizeequal to or exceeding about 15 microns and not larger than about 60microns.
 22. The method of claim 21 wherein the average particle size ofthe additives is in the range of about 15 to about 35 microns.
 23. Themethod of claim 21 wherein the average particle size of the additives isin the range of about 20 to about 30 microns.
 24. A micaceousglass-ceramic for use in the fabrication of a dental restorationcomprising a variety of colors and shades to adequately match the colorand shade of a patient's teeth in the mouth wherein the glass-ceramic ismanufactured from glass and additives selected from the group consistingof pigments, fluorescing agents, opacifying agents and mixtures thereof,and whereby the additives have average particle size equal to orexceeding about 15 microns and not larger than about 60 microns.
 25. Themicaceous glass-ceramic of claim 24 wherein the average particle size ofthe additives is in the range of about 15 to about 35 microns.
 26. Themicaceous glass-ceramic of claim 24 wherein the average particle size ofthe additives is in the range of about 20 to about 30 microns.